1. Field of the Invention
The present invention relates to an air-conditioner and, more particularly, to an apparatus for controlling a speed of a fan motor of an air-conditioner.
2. Description of the Conventional Art
In general, a single-phase induction motor is used as a fan motor of an air-conditioner. In order to generate rotating torque, the single-phase induction motor supplies a magnetizing current generating a rotating field and an induced current generated from a rotor to windings connected with an external power terminal.
The single-phase induction motor has a limitation in enhancing efficiency due to a primary copper loss of a stator and a secondary copper loss of the rotor.
In order to resolve such limitation, recently, a HIM (Hybrid Induction Motor) as shown in FIGS. 1 and 2 is used as a fan motor of the air-conditioner.
FIG. 1 is a schematic sectional view of the HIM in accordance with a conventional art, and FIG. 2 is a schematic sectional top view taken along line B-B′ of the HIM of FIG. 1.
As shown in FIGS. 1 and 2, a bracket 104 of the conventional HIM 100 includes a stator 105 and an induction rotor 101 installed at an inner side of the stator 105. A plurality of slots 108 are protrusively formed at an inner side of the stator 105 and coils 103 for applying a current are wound at the slots 108.
Aluminum rotor bars 112 are vertically inserted into a plurality of air gaps formed in an up/down direction at an edge of the rotor 101, and the aluminum rotor bars 112 are connected by an end ring 102.
A rotating shaft 109 for transferring a rotational force of the rotor 101 to outside is installed in an air gap 110 formed at the center of the induction rotor 101. The rotating shaft 109 can be rotated by an oilless bearing 107 installed at the bracket 104.
A permanent magnet rotor 106 for rotating the rotor 101 with a strong magnetic flux while being rotated by rotating field generated from the stator 105 is installed between the stator 105 and the induction rotor 101.
When an AC voltage is applied to the conventional HIM, the permanent magnet rotor 106 is rotated by the current applied to the coil 103 of the stator 105, and the rotating permanent magnet rotor 106 generates a rotating field with strong magnetic flux, to rotate the induction rotator 101. At this time, the permanent magnet rotor 106 in a low inertia state is separated from a fan (not shown) and rotated owing to the rotating field of the stator 105, and as a torque generating magnetic flux is supplied to the induction rotor 101 owing to the rotating field of the permanent magnet rotor 10, the induction rotor 101 is rotated.
In other words, when the permanent magnet rotor 106 is rotated by the rotating field in an oval form generated from the stator of the distributed windings, the permanent magnet rotor 106 generates rotating field with strong magnetic flux to make the induction rotor 101 rotated, so that the HIM is operated with high efficiency and low noise.
Velocity characteristics of the conventional apparatus for controlling a speed of the fan motor of the air-conditioner and a general induction motor will now be described with reference to FIGS. 3 and 4.
FIG. 3 is a circuit diagram showing the construction of the apparatus for controlling a speed of the fan motor (HIM) in accordance with the conventional art, and FIG. 4 is a graph showing speed characteristics of the conventional HIM and a general induction motor.
As shown in FIG. 3, when the apparatus for controlling a rotational speed of the fan motor by controlling a phase of a voltage applied to the fan motor (HIM) through one triac is applied for the HIM, a speed control range (i.e., 790˜880 RPM (revolution per minute) according to the voltage is limited as shown in FIG. 4. Namely, the speed control range is limited to the 790˜880 RPM(880 RPM−790 RPM=90 RPM) due to the permanent magnet rotor 106. This causes a problem that the conventional apparatus for controlling the speed of the fan motor cannot be applied for air-conditioner which requires a speed control range or above 100 RPM.
U.S. Pat. No. 6,819,026 issued on Nov. 16, 2004 also discloses an induction motor used as a fan motor of an air-conditioner.